Coded track circuit signaling system



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June 6, 1944. H. s. WYNN l CODED TRACK CIRCUIT SIGNALING `SYSTEM Fi'id' Nov. 21. 1942 9 sheets-sheet 9 (TTI:

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Patented June 6; 1944 UNITED STATES .PATENT .OFFICE SYSTEM v Harold S. Wynn,'Pittsford, N. Y., assignor to General Railway Signal Company, Rochester, N. Y

'Application' November 21, 1942, Serial No. 466,406

24 claims This invention relates to coded track circuit signaling systems for railroads, and it more particularly pertains to a system for single track railroads used in combination with centralized traiic control.

The general organization of the system provided by the Ipresent invention is that the automatic control of signals'space'd alongy a single track railwayhaving passing sidings is eiTected by the transmission of continuous coded controlsthrough the ,track rails of the varioustrack sections between signalvlocations The groups of signals which; are located adjacent the ends of the passing sidingsarefsubject to manual control from a eentral'fcontrol oce. Such groups of signals, Atogether with the' field apparatus for their control, are conveniently called field stations. Although'the signals at the re` spective eld stations can be controlled manually from the control'olce by direct wire control, in most cases where there are several ield stations involved, for the purpose of saving line wires, it is more desirable that a code type communication systembe employed as is shown, for example, in the .patent to Judge et al., No; 2,082,544, dated June l, 1937, or in the patent to Hailes et al., No. 2,259,561, dated October 2l, 1941. Y

The presentvinvention is an improvement in the coded trackL circuitfsignaling system disclosed in the prior applicationof Judge, Ser. No.A

455,922, filed August 24, 1942, and no claim is-V made herein to that Vwhich is disclosed in such application. Y Y .v v.

,An objectief thepresent Vinvention is toprovide a system of self-coding ina track circuit whereby .code impulses vare transmittedlin both` The transmissionvr of each impulse isV dependent upon` a Vpreceding impulse Atram-- mitted from the opposite end of z-the track sec-- tion in that the duration yo1? theimpulse is timed;

forvexample, byl the-drop-away time of a track repeater relayv picked upby :such' .preceding im= pulse, thus causing the-track. circuit to be self-fV Another obj ect Iolf :prese-nt -invention 4isV to employ self-codinginjv the -coded-track circuits normally as afpotential tumble-down medium by which opposing manuallyjfcontrolled Vsignals-` can be interlocked for eitheiuseleted;direction of traffic without requiring AtheV use of special traffic direction control relays Vfor governing the direction of code transmission. Y y f Another object of the Apresent invention is tol materially slow vdown thecoding inthe track sections whenthere areV no routesfestablished as compared to and 180 coderates selectively applied for the control of signals in estab-u lished routes. The code is ,materially slowedv down by using the dropaway time Vof a slow acting track `repeater relay to,` measure the length of the respective'impulses traiismitted from each end Aof each otjthe .track sections, although it is toib'e understood that other control means canbe employedtor measuring the length of the impulsesrtransmitted. Inv this manner, a slower code may be transmitted normally than is practical to produce by yacude oscillator, thus materially reducing the number of relay operations required and prolonging the life of the coding apparatus. t

Another object voffthepresent invention is to control the directionalV stick relays for the'interfA mediate signals'ina stretch of track between passing sidings in such amanner as to cause them to be picked up upon tumble-down of relays for the opposing signals, but to bedropped away in the rear of la train as it progresses through the stretch oftrack. l Another object of the present finvention 4in connection with restoration to the normal conditions of self-coding for4 the track section in the rear of a train is 't'o" cause self-coding impulses to be 'rst Vin'tfer'sper'sed among opposing" impulses formed by a' '75' code oscillator, such 75 code impulses being transmitted in adirfectionto govern signals forfafollowingr train," and' then cause self-coding"impulses'to bet'ransmitted in both directions vwhen lthe 'train vpro? gresses through the next block, Vthe shift to both directions of self-*coding being' effected at a time lto insure the continued transmission of4 Self-COdiIIg' impulses inbothv directions'. f "1 Another object of the'A present invention when self-coding impulsesv are" interspersed amongVl impulses repeated from a '75 icode oscillatorr and' transmitted inthe 'opposite direction, is that' the self-coding impulses 'be'of "such a length, together with a unique track'circuit` organization;

actually transmitted. Vi a VOther objects, purposesivandcharacteristicfV ence will be made to the accompanying draw-` ings in which those parts having similar features and functions are designated through the several illustrations by like ,letter reference characters whichV are generally made distinc-r tive by reason of preceding numerals indicative of the location of the signal with which such parts are associated and in which:

Figs. 1A, 1B and 1C when considered to gether illustrate means for communicating manually designated switch and signal controls from a control office to a pluralityof eld stations, together with circuit means at the iield stations for yreceiving and storing the controls communicated from the controlofce;

Figs. 2A, 2B, 2C and 2D when placed end to endrespectively illustrate the manner inrwhich coded track circuits are applied to the control of the signals for this yembodiment ofthe pres-r ent invention; Y.

Figs. 2D and 2A when placed end to endV respectively illustrate the circuits linvolved in the transmission of track circuit codes through a siding section;

Fig. 3 illustrates in detail the Amanner in which approach locking' relays are controlled for the signals at a typical eld station of this 4ernbodiment of the present invention;

Fig. 4 illustrates the manner in which approach lockingvis applied in governing thepower operation of a track switch Vto provide for its safe operation, together-with the control of correspondencev relays associated `with that track switch;V K

Fig. 5 illustrates circuits typical of those employed for the control of code forming oscillators at each of the signal locations; Y

Figs. 6A through 6M (letter I omitted) illustrate Vdiagrammatically Vthe conditions of track circuit codev transmission Yfor the various track sections under certain typicalrconditions of train operation; y y y Fig. 7 illustrates diagrammatically how selfcoding impulses are formed and transmitted under normal conditions of the system; and

Figy illustrates diagrammatically how sel-E- coding impulses areformed and transmitted al'- ternately with code impulses formed by sa 75 oscillator and transmitted from the opposite end ofthe track section as a step in the process of restoration to the normal conditions of self-codingfin therear of a train. y

The illustrations employed in the disclosure of this Yembodiment `of the present invention' have been arranged to facilitate the disclosure as to the mode of operation and the principles involved rather than for the purpose of illustrating the construction and arrangement of 'parts that would be. employed in practice. 'Thus the relays and their'contacts Vare shown ina conventional manner, certainrelay contacts' being shown Vin written circuit form and identified as of yparticular relays by vcorresponding reference characters appearing directly Aabove such contacts. y

The symbols'fl-i) 'and are employed' toY indicate the positive and' negative terminals re-v spectively of suitable batteries-or other sources of direclt vcurrent,"and VtheV circuits with which those symbols are used always have current nowing in the same direction.'

In order to simplify the description of the present invention, reference is made from time to time to functions common to all parts of a similar character by use in the description of letter reference characters without their preceding numerals for the designation of such parts. It is to be understood that such a reference applies to any parts designated in the drawings by reference characters thatare similar except for numerals preceding the letters.

'Ihe trackway for which this embodiment of the present invention is'provided comprises a main stretch of track divided into several track sections and having associated therewith passing sidings A and B (seeFigs. 2A through 2D). The right-hand end of the passing siding A is connected to the main track by a track switch 2W, and the left-hand end of the passing siding B is connected to the main track by the track switch 3W. Associated with the track switches 2W and 3W are detector or OS track sections 2--3'1 and il-ST respectively. Between the passing sidings A and B are track sections 2-5T, 4-1T and G-ST, each of which has a coded track circuit. It is to be understood, and it will be `readily apparent as the description progresses, that the number of track sections in the stretch of track between the passing sidings A and B can be increased or decreased in accordance with the requirements of practice. There is a track section in the portion of maintrack that isV associated with each of the passing sidings which is conveniently calledfa siding section. Track section 8-||T,"for example, is a siding section associated with the passing siding B. I

Associated with the lright-hand end of the passing siding A are manually controlled signals 2A, 2B, 3A and 3B, signals 2A and 2B vbeing starting head-block signals governing entrance into the stretch of track between the passing sidings, and signals 3A and `3B being entering signals for governing train movementsinto the siding section and into thefpassing siding rc spectively. In a similar manner signals 8A, 8B, 9A and 9B are associated `with the left-hand end of the passing siding B. Intermediate signals 4, 5, 6 and 1 are included in the stretch of track between the passing sidings A and B, signals 4 and being provided for governing eastbound irafc (to the right) and signals 5 and 'l being provided for governing westbound traflic (to the left).

Although the signals illustrated in this Iem-k bodiment of the present invention are of the type having individual color lampunits for the respecsignals, position light signals, or search light sig-v nals could aswell be employed in accordance with thev requirements of practice. l

Each ofthe track vsections'in the 'stretch of track between the Ypassingv sidings A and B, andeachV of thesfiding sections has la coded track circuit which includes at each'end a code followingtrack relay 'TR and a source of current. For the purpose of obtaining the best operating characteristics of the code following Ytrack relays, andV for' the purpose of providing brokendown joint protection, it .is desirable thatfeach of such relays have a'polarstr'ucture sonarranged as Vto cause the relay contacts to'be biased to a deenergized positiorilfrom which they can bemoved only upon energization Aoi" they relay windings with aparticularv polarity. 'Y i Associated with each of the track relays TR is a code following trackrepeater Vrelay 'I'P which is used primarily to lighten the contact load of the track relay .TRwith which it is associated. Thus the contacts of each of the relays TP are used for governing the energization of a distant control relay D through the medium of a decoding transformer, the energization of a front contact repeater relay FP;"fthe energization of a front and back contact repeater relay FBP, andthe energization of a home control relay H. Of this group of relays, the relay D is responsive only to a 180 code rate, the relays FBP and H are sufficiently slow in'dropping away to be maintained der normal conditions of the system. The relay FP is quick is picking up but is sufficiently slow in dropping away to measurethe desired length of theself-coding impulses. By this arrangement the slow drop-away characteristics of the FP relay will cause such relay to be maintained steadily picked up when a 180 or a 75 code is received by the associated track relay TR.

Suitable driven code forming devices are provided for the respective signal locations for forming the 180 and '75 code rates employed for the control of signals in" established routes. Although it is to be understood that motor driven codesor other code forming devices could be employed, the driven codes are formed in this embodiment of the present invention by code oscillators which can be of a structure such as is shown, for example, in the application of O. S.

Field, Ser. No. 369,862, dated December 12, 1940.

An oscillator of such nature is capable of forming but one code, thus requiring separate oscillators for forming thek180 and- 75 code rates respectively. It is therefore provided that 180 and 75 code oscillators |800 and 15C respectively are provided for each of the field stations and each of the intermediate signal locations. Such oscillators are normally inactive but their operation is initiated upon the establishment of a route including a signal at the location with which such oscillators is associated.

At each end of each of the coded track circuits is a code transmitter relay CP which is normally active in the transmission of impulses formed by self-coding means dependentupon the drop-away time of the relay FP for that end of the track circuit. Each relay CP is active for the transmission of self-coding impulses because of the energization of the H relay associated with that end of the track circuit. but upon the dropping away of that H relay, the relay CP becomes active for the transmission of a '75 or a 180 code as selected.

At each of the field stations, relays LGZ, RGZ,v

B, WN and WR (see Figs. 1B and 1C) are provided as relays subject to manual control from the control oce. Of these relays, the relays LGZ and RGZ control the clearing of signals for governing westbound and eastbound traffic respectively, the relay B is employed in the manual restoration of a signal to stop. and the relays WN and WR are employed in governing the power operation of the `track switch at that lield station to respective normal and reverse positions.

vAssociated with the safe operation of the'power track switch at each end of each of the passing sidings are approach locking relays AS, signalat-stop relays M, a switch point repeater relay WP, and correspondence relays NCR. and RCR as illustrated in Figs. 3 and 4. The correspondence relays NCR: and RCR foreach of the track switches have contacts included in the control circuits for the signal `control relays AG and BG (see Fig..2A) associated with the signals at that field station. Each intermediate signal has a directional stick relay S employed in the control of signals for following train movements.

Having thus considered the general organization of the control apparatusemployed in this embodiment of the present invention, a consideration will now be given to the mode of. operation ofthe system under typical operating conditions.

, Operation Gencml-1t is believed expedient before considering in detail the circuit organization of this embodiment of the present invention, to point out, with reference Vto'the diagrams of Figs. 6A through 6M,`the general mode of operation of the system and the objects accomplished thereby.

With reference to Fig. 6A the normal conditions of the system are illustrated. The normal conditions of the system are assumed to be those conditions which exist when the trackway is unoccupied, and when there are no routes established. Under such conditions the manually controlled signals ateach of the field-stations are at stop, the intermediate signals 4, 5, 6 and 'l are at caution, and the power track switches of the sidings are in their normal positions as would be required for the alignment of routes for through train movementson the'main track.

Normally, self-coding is eiective in each of the coded track circuits as a potential means for interlocking the opposing manually controlled starting head-block signals governing entrance to the'stretch of track between passing sidings, and the opposing manually controlled signals governing entrance to the siding section associated with each of the passing sidings. By this means, impulses of preferably a length substantially twice that of the length of a code impulse are transmitted contemporaneously through each of the track sections having a coded track circuit, the impulses for both directions being transmitted in alternate relationship with each other. In this manner, it is provided that any one of the manually controlled signals can be controlled to indicate proceed, and upon the communication of such a control from the control oflice; an opposing signal interlock is set up by causing the tumble-downV of the code transmitters supplying self-coding to the track circuits used in the control of opposing signals, such tum.- ble-down being effective through each 'successive track section to the next opposing manually controlled signal. Upon the tumble-down becoming effective, as is illustrated in Fig.v6B where it is assumed that a control is transmitted for the clearing of signal 2B, a driven code is transmitted through leach of the track sections through which the tumble-down has become effective to control the signals involved in the establishment of the route, such code being at a 75 or a 180 rate in accordance with the proceed or stop indication of the signal governingentrance to the adjacent track section. VThus in Fig. 6B a 75 driven code is transmitted from right to left in the track section'G-ST because of the signal 8A1'being at stop; a v driven code istransmitted from right to left in the track section 4-1T in accordance` with the proceedindication of signal-6; and-a- 180 code is transmitted from right to left in the track section 2-5T because of the proceed indication of the signal 4. In accordance with vthe reception of the 180 driven code at the left-hand end of the track section 2-5T, the signal 2B is controlled to indicate clear after the track switch 2W has been properly power operated to its reverse position.

With reference to Fig. 6D, a condition is illustrated in which an operator is assumed to have proceeded further in the establishment of a route for an eastbound trainby causing the signal 8A to indicate proceed. The communication of a control for the proceed indication of such signal from the control oice is effective to cause the cessation of the transmission of self-coding impulses from left to right in the siding section 8-IIT, such cessation providing lan interlock to insure the maintaining of the opposing signal IIA at stop. The cessation of the self-coding causes the dropping away of the H relay at the right-hand end of that siding section, and the dropping away of such relay causes the transmission of a '75 driven code from right to left in the track section because of the stop indication oil signal HBA, such 'l5 driven code being effective to cause the signal 8A to indicate caution.

The diagrams of Figs. 6D through 6G illustrate the conditions of restoration of the system of code transmission to normal in the rear of an eastbound train as it progresses along the trackway. It will be noted in Fig. 6E, that a step in restoration to the normal conditions of code transmission for the track section 2--5T in the rear of the eastbound train is a condition in which code impulses measured by the oscillator 15C are transmitted from right to left in the track section, while self-coding impulses of substantially greater length are interspersed alternately among the 75 code impulses. Under such conditions, only alternate 75 code impulses of the oscillator 15C at the right-hand end of the track section 2-5T are transmitted, as the other impulses are reffectively blanked out by the self-coding impulses transmitted from the opposite end of the track section. This condition is diagrammatically illustrated in Fig; 8 and will be hereinafter considered more specifically in connection with the detailed description of the circuit organization.

It will be noted in the diagram of Fig. 6F that as the eastbound train progresses so as to vleave the track section d-'IT unoccupied in the'rear of the train, the conditions of code transmission in such track section are established to correspond with those just described for the track section 2-5T, but the conditions of self-coding in the track section 2-`5T are restored to normal so as to cause self-coding impulses to loe-trans'- mitted in both directions. This change is effected in accordance with the dropping away of the stick relay 4S associated with signal 4, such relay being restored by the picking up of the H relay for the left-hand end-of the track section d-lT uponV the reception of the code impulses transmitted fromv right to left in the track section li-IT.

SeZf-codz'ng.-In a coded'track circuit system of the type under: consideration, it is desirable to provide for transmission of current pulses at recurrent intervals in both directions. over the track rails of the various track sections for detectionv of occupancy. of such track sections by a train and for relaying a tumble-down control'.

"Inaccordance'with the present invention, this is accomplished by an operation conveniently termed self-coding, as distinctive from the type of system, such as disclosed for example, in the prior application of T. J. Judge, Ser. No. 365,669, rlled November 14, 1940 employing driven code pulses in one direction in conjunction with inverse or off-code pulses in the opposite direction, and also the type of system such as disclosed in the prior application of T. J. Judge, Ser. No. 455,922, filed August 24, 1942 employing driven codes of different rates for opposite directions to create a beat code condition. In the so-called self-coding organization of this invention, current pulses are transmitted alternately in opposite directions over the track rails of each track section, once such self-coding operation has been initiated, as a result of the intermittent energization of a code following track relay at each end of the track section by the current pulse received from the opposite end, and without the use of code oscillators or equivalent intermittently operated contacts for forming code pulses. The duration of these current impulses in opposite directions under such selfcoding conditions is determined by the operating time of a suitable relay means governed by each track relay; and while the length or duration of these current pulses may be adapted to different operating conditions as desired by varying the operating time of such repeater relays, in the present embodiment it has been assumed that these pulses will vbe in the order of .8 of a second. Y In this connection, it should be understood that the release time of the code responsive or signal control relays, such as 2H in Fig. 2A,is sufliciently long to maintain its contacts closed by the operation of the associated track relay at recurrent intervals of such .8 of a second. The current pulse for each direction is transmitted when the current pulse for the opposite direction ceases after a brief interval corresponding with the release time of a quick-acting track relay and pick-up time of a quickacting transmitter relay.

Fig. 'l shows diagrammatically in the form of a time chart the relative timing in the operation of the relays associated with the opposite ends of the track section 2-5'1, together with the direction and duration of the current pulses in the track rails of this track section. In this explanatory diagram the vertical lines of the graphs for the several relays indicate a change between the open and closed condition of the contacts of the corresponding relay, the inclined lines associated with such vertical lines indicating the time involved for such operation of the contacts to occur after the circuit for the winding of the relay is opened and closed. The horizontal lines of the graphs in Fig. 7 indicate the time duration of an unchanged open or closedfcondition of the'contacts of such relays, the elapse of time being from left to right. l

Referring to the explanatory diagram of Fig. 7' and disregarding for the present how the socalled self-coding condition was created, assume that aV current pulse transmitted from left to right over the track rails of track section 2-5T has just ceased, and the track relay STR 'has just become deenergized, as. indicated at the left in Fig. 7. The repeater relays STP and EFP are energized at the time the track relay ETR,V releases and hence Yclosing of aback Contact of thertrackrelay STR causes energization of the transmitterrrelay 5G12I in the manner Vdescribed in .detail later andy indicated wby the dotted line asados? Ato the track rails of the track section 2`ST to transmit a current pulse in the opposite direction. When the track relay STR releases, it deenergizes its repeater relay STP (not included in the timing diagram in the interests of simplicity) and in turn the repeater relay SFP which is made slow releasing by a rectifier, and after the slow-release time of relay SFP the circuit for the transmitter relay SCP isvbroken to terminate this current pulse vas indicated bythe dotted line 4| in Fig. 7. Thus, the deenergization of the track relay STR causes transmission of a current pulse of a. limited duration towardv the opposite end of the track section.

This current pulse thus created by the deenergization of track relay STR and energization of transmitter relay SCP, causes energize.- tion of the track relay 2TR at the otherr end of the track section, and in turn its repeater relaysl 2TP and ZFP; and when this current pulse ceases, the track relay 2TR drops and causes -energiza'- tion of the transmitter relay ZCP to apply a current pulse at that end of the track section, as indicated by the dotted line 42 in Fig. '7.V This current pulse from left to right continues until a repeater relay 2FP drops, whereupon the transmitter relay 2CP is deenergized as indicated by the dotted line 43 in Fig. `'7.

This same operation -just described is repeated over and over under the normal self-coding conditions under consideration, as thetrack relays for the opposite ends of the track section are automatically energized and then released by current pulses coming from the other end. It can be seen that these current pulses are self-generated, so to speak, with their duration and spacing determined bythe characteristics of the track circuit and the operating times of the relays, as distinctive from the usual form of code transmission in coded track circuit systems where the duration and spacing of the code pulses are determined directly orindirectly by contacts in'- termittently operated by a motor driven coder or by a code oscillator at some xed code rate,` such as 75 or 180 times per minute, such coding contacts being ordinarily arranged to give substantially equal duration and spacing of code pulses. The transmission of code pulses alternately in oppositel directions by such a self-coding op'- eration serves to maintain energized a suitable code responsive means at both ends of the track section such as the slow-release signal control relays'ZH and SH, and thus detect at both ends of the track section occupancy of that track sec.- tion, and also alox'd a medium for relaying a tumble-down control in both directions for single track signaling. The self-coding condition 'above explained exists while Vthe signal control, relays 2H and SH at both ends of the track section are energized; and when one or the other of these relays 2H or SH is deenergized by stopping transmission of code pulses toward the corresponding end of the track section in a manner later explained, the code pulses' transmitted fromV such end of the track .section are changed-to driven code pulses lof a selected rate derived from a suitable code oscillator or the like. These driven code pulses of` a selected code rate which exist Vwhen coding in the opposite .direction is cut off, not onlyserve togovern the Vindication of signals Vwithout .interference'in Vaccordance with the codev rate butA also yact to initiate. ka restoration to the normal self-coding conditions end. This conditionis illustrated 'in theb after train movement and the like. In this connection, it can be Vseen that the self-coding conditionV above explained is due to the fact that the track relay at a given end of the track section, when energized by a current pulse from the opposite f end, sends a code pulse toward' such opposite end, thereby creating conditions at such opposite end to return anotherv current pulse;

and once this operation is initiated by the en` ergization of the track relay at eitherV end-of the track section, such self-coding operation Willcontinue until the transmission of code pulses toward either end of the track section is in some way cut off, and the track relay at that end is no longer energized. A g

Under certain conditions of train movement as later explained, driven code pulses at a'caution code rate may be maintained for a time in one direction in a track sectioninterspersed or separated by self-coding pulses from the opposite explanatory diagram of Fig.`8.l Y' y v i Having thus vdescribedina generalmanner the mode of operation ofthe relays associated with the generation of self-coding impulses for a typical cycle of operation of selfcoding,-a more detail description will now be set forth as to the circuits involved in providing such mode of operation. A 'A Y Assuming the-.relay ZTR (see Fig.- 2A) --tofbe dropped away at the termination-of an impulse transmitted from right to left in the track section 2-ST, so that the dropping awayofrelay 2TR by the closure ofback'contact is eiective to cause the picking up'of ythe relayV ZCP for initiating the transmissionof aself-coding'impulse from left to right inthe track section',-the relay 2CP is picked up by the 'energizationof' a circuit extending -from including frontv front contact S0 of relay ZCP, the lower rail of track section 2-ST, back contact Sl of relay SCP (see Fig. 2B), Winding of relay STR, and upper rail of track section 2-ST to the negative terminal of track battery 49. The picking up of relay STR closes an obvious circuit at front contact. 52 to cause the picking up of the relay STP, and the picking up of such relay causes the picking up oirelay' SFP by the closureof an' obvious, circuit at front contact S3. Whenk relay SFP is picked up, a ,circuitis closed for' the,

relay SHeXtending `from vincluding front contact S4 Vof relay STP, frontcontact;SS 'of relay SFP, front contact S6 of relay SFBP, winding lof relay 5H, and back contact S1 ,ofjrelay 47S, to

At the left-hand end' tof the track 'sectiolrif 2TP. (see' Fig. 2A) by '.the opening of front con-- tact .48, .and theopening ofY frontcontact S8V of relay ITP deenergizes the relay 2FP, but, 'because ofsuchrelay having its winding. shunted'. by a `half-Wave rectierior. because of. thefrelay having other means formaking it slowin 'drop-4` ping`away),.the.` relay 2FP maintainsvits frontcontact in the circuit for relay 2 CP closed for measuring the length of the impulsebeing transmitted from left to right in the track section 25T. The dropping away of the relay 2TP under such conditions opens the circuit for relay 2H, but such relay is sufficiently slow in dropping away to be maintained steadily picked up during the orf periods of code transmission from right to left in the track section. Y

When the relay ZFP is dropped away after measuring the length of the impulse transmitted from left to right in the track section 2*- 5T, the opening of front Contact 44 is effective t0- cause the dropping away of the relay 2CP for the termination of that impulse. rl'he dropping away of the relay 5THl because of the opening of its circuit at front contact 50 ofv relay 2CP, causes the dropping away of the relay ETP, and the droppingaway of that relay causes the picking up of the relay 5CP.for initiating the transmission of a self-coding impulse from right to left in the track section 2-5'1. lThe circuitv by which the relay SCP is picked up under such conditions extends from including iront contact 553 of` relay 4FBP, front contactJ 69 of relay SFP, front contact 6| of relay 5H, winding of relay 5CP, back contact 52- of relay 5S, and` back contact 52 of relay 5TR, to

The dropping away of relay STR causes the dropping away of relay'5TP by opening front contact 52, and the dropping away of relay ETP causes the deenergization of relay 5Fl.p by opening front contact 53. The dropping away of relay STP is also effective to open the circuit which has been described for the relay 5H at front contact 54, but such relay is maintained picked up by its slow-acting characteristics, it being suciently slow to bridge the orf periods of the code normally transmitted from left to right in the track lsection 2 -5T. The closurel of back contact of relay 5'IP- prior to the droppingaway of the relay 5FP provides a circuit for the energization of the front-back repeater relay EFBP, such circuit extending from including back contact 53 of relay STP, frontcontact 63 of relay SFP, and; winding of relay 5FBP, to The relay 5FBP has suiiiciently slow drop-away characteristics to cause-that relay to be main-` tained picked up during the on periods of the code normally transmitted from left to right in the track section 2l-5T.V

At ythe left-hand Vend of the track section 2 5'1, the relay 2'I'R is responsive to the impulse initiated by the closure of front contact 5| of relay 5CP. TheY track circuit by which relay 2TR is energized extends from the-positive terminal oi"v track battery 64 including front Contact 5| of relay ECP, lower rail of track section 2-5T, back contact 50 of relay 2CP (see Fig. 2A), winding of relay 2TH., and upper rail of track section 2-5T tothe negative terminal (see Fig. 2B) of track battery 64.. In accordance with the picking of relay ZTR (see Fig. 2A), the closure of front contact 48 causes the picking. up of relay 2TP, and the picking up of such relaycauses the lpicking up of relay ZFR by the energization of .an obvious circuit upon the closure of a front con-v tact 53, the opening of backcontact 53 being effective to open the circuit for the front-back repeater relay ZFBP, but such` relay is sufficiently slow in dropping away to be maintained steadily picked up during `the on periods of the code normally transmitted from right to. left at the` trackv section 2 5-I". 'Upon vthe picking uporrelay ZFP, a circuit is closedforthe.relayZHex; 7,5

tendine from (+L irlludrigv front Contact 55 of relay ZTP, front contact 6.6 vof relay ZFP.- front contact 61 of relay ZFBjP and winding of relay 2H, to Relay 2H is sufficiently slow in dropping away to be maintained steadily picked up during the off periods of the codes normally transmitted from right to left in the track section 25T.

At the right-.hand end of the track section 2- 5T (see Fig. 2B) the dropping away of the relay 5Fl upon completingthe timing of the selfcoding impulse transmitted from right to left in the track section Z-ilT, opens the circuit which has been described `for the relay ECP at front contact B to cause such relay to be dropped away and terminate the impulse by the opening of front contact 5| in the track circuit. The ter; mination of the impulse. causes the dropping away of the track relay 2TH (see Fig- 2A) at the left-hand end of track section,- and the dropping away of such relay, by the closure of back contact 48, causes the picking upoi relay 2CP for the transmission of the next impulse from left to right in the track section 2 5T, such relay being picked upbythe energization of a circuit which has been described, for` the initiation of a second cycle of operation corresponding to that which has just been considered'in detail.

Clearing of starting head-block signal-If, for example, an operator desires.` to cause the clearing of the starting head-block signal 2B for governing passage of a train out of the passing siding A into the main stretch of track between the passing, sidings A and B, he actuates the switch control lever ZSML (see Fig. 1A) at the control ofce toits right-hand position for the power operation of the track switch 2W to its reverse position, and he also operates the signal control lever 2-3SGL to its right-hand position to cause the clearing of a signal at iield station No. l governing traflc to the right. In accordance with the operation of lever 25ML to its right-hand position, a circuit is closed at contact 68 of such lever to apply energy to wire 24 for communication of a control to field station No. 1 Afor the picking up of the re1ay2Wll...l In accordance with the communication of the control from the control office to eld station No. 1

for the operation of the track switch 2W to its,

reverse position, energy is appliedY to Wire 24 (see Fig. 1B) at such eld station 4for the energization of a circuit for the relay 2WR including the upper winding of that relay, back contact 69 of relay SLGZ, and back contact 10 of relay ZRGZ, to Relay is maintained picked up by a stick circuit extending from (-1-), including back Contact. |82 of relay ZWN, front contact |83 of relay ZWR, and lower winding of relay ZWR, to Y The actuation of the lever 2 -3SGL (see Fig. 1A) toits right-hand position applies renergy upon the closure of contact 1|. of such lever in its right-hand position to wire 23 for the communication of; a control rtoeld station No. l for the application4 of energy to. wire 23V at such iield station for the energization of the lower winding of relay ZRGZ. The circuit by which venergy ap-` plied to wire 23 at eld station No. 1 causes the energization of the 'lower winding of relay ZRGZ includes an interlocking back contact 12 of theV relay, SLGZ for controllingopposing signals.- A a stick circuit for maintaining relay 2RGZ picked up is closed from including front contact |84` of4 relay 2'-.3TR, connected in multiple with back contact |85 of relayA 21-.3TP, "back Contact l 18| of relay 2-3B, front contact |86 of relay Z-RGZ, .and upper winding of relay ZRGZ,

. Upon the picking up of relay ZRGZ, the cir- "cuitV by which the relay 2CP (see Fig. 2A) has been Aactive for the transmission of self-coding impulses isopened at back contact 45 to render such relay inactive. At the right-hand end of the track section 2-5T, the cessation of the pulsving of. relay STR (see Fig. 2B) causes the cessation of the pulsing of relay T'P by the opening of front, ,contact 52, and the cessation of the pulsing of relay SIP'causes the cessation of the pulsing of relay, 5FP because of the opening of its circuit ati-ront contact 53. When relay 5FP is inactive the circuit for relay SFBP is opened at front contact 03', andthe dropping away of that relay opensV the circuit at front contact 'I3 by which the relay 4CP has been normally active for thev transmission of 'self-coding ,impulses from left to right inthe track section 4-'|T. The circuit by which irelay 4CP has been active extends from (fl-),including frontV contact 13 of relay 513B?,y frontcontact 14 of relay 4FP, front contact `|52 of relay 4H, winding of relay fiCP,V back contact ,Alliv of relay 4S, and back contact 'l1 of relay-4IBgto v Thedropping away ofrelay SFBP under such conditions vvalso closes a circuit to cause the picking up of the stick relay 4S associated with signal 4. Such circuit extends from including front contact 78 of relay 4FBP, back contact 'I9 .of relay EFBP, back contact 30 of relay 5S, and

winding or relay 4S, to

At the right-hand end of the track l.section 4)-"l-T, the cessation of code transmission from left-to right inthe track section causes the relays 'lTR and lTP (see Fig. 2C) to be rendered` inactive,l and the failure of relay ITP to pulse contact 8| causes the cessation of the pulsing of therelaylFP, and the inactivity of such relay.

of relayFP; front contact 85 of relay 6H, winding of relay GCP, back contact 8Sv of relay 5S, andback contact 81 4of relay STR, to

, The.dfrf opping away of relay lFBP also closes agcircuit'for the energization of the stick relay BS associated with signal 6. Such circuit extends lfrom(-l), including front contact 88 of relayfGFBP, backV contact 8S of i relay 1FBP,

backy contact S0 4of relay 11S,4 andwinding of relay'6S, to Y ,l

The cessation of code transmission from left toright in the track section G-V-ST renders the relays- STR and STP (see Fig. 2D) inactive, and the cessation of the pulsing of` contact Sl inthe circuit offrelay SFP causes thatrelay to become inactive;A jIhe cessation ofthepulsing of relay SFPpuponthe opening .of iront contact S2 causes' th 'dropping awayofrelay SFBP, andthe relay also dropped away bythe opening of its circuit'whichis normallyclosedduring leach impulsev of 'acode' received by the track relay STR, such circuit, extending from (+L including front contactjSSlIof relay'S'I'P, front contact S4 of relay of relay SH', to'() The dropping away of relay 9H' upon the opening of front contacts S6- and Sl provides an opposing signal interlock to prevent the picking up of the relays SAG and SBG respectively if an operator were to attempt to' cause the clearing of signal SA or signal 9B.

The relay 5H (see Fig. 2B) at the right-hand end of the track section 2-5T is dropped away because of the termination of the pulsing of contact 54 of relay 5'IP, such relay being normally energized during each` impulse received by thev track relay 5'IR'by a. circuit which has been described. The dropping away of relay 5H opens a circuit which is;normally closedfor the yellow lamp of signal 5 at front contact S8.`v Such circuit is normally closed from including front con-'- tact S8 of relay 5H, back Contact 9S of relay 5D, and the yellow lamp Y of signal 5, to (--).A The redIlamp of signal 5 is illuminated by the energization of an obvious circuit closed at backcontact S8 of rrelay 5H.' Yi f In accordance'withthe droppingaway. of the relay 5H,i the relay 5CP.is. rendered active to transmit a driven code, suchcodebeing of a 180 or a 'l5 rate as selected by contact |00 of relay 4H. The circuitV by .which lrelay .SCP is active for the transmission of a 18() code, as selected by. the closure of front .contact |00 of relay 4H, ex-

tends from (-1-), including contact |0| of oscillator |C, front contact |00 of relay-4H, back.

. contact 6| of relay 5H, winding of relay Y5CP, back contact l62 of yrelay 5S, and vback lcontact 52of relay5TR,to (-').l 1 s In a similarr manner, at theV right-hand end of" track section 4--|T, the .relay A'IH .(see Fig. 2C) is, dropped away whenrelay lTP. is rendered ina-c-` tive, such relaylH beingnormally energizedfor each impulse ofthe code received by relay 'lTR because of the closure of a circuit extending from including front contact |02 of relay 'l'TP ,front contact |03 ofrelay TFP,` front contact |04y of relay 1FBP, winding of relay 1H, and back con- The dropping awayv tact |05 of relay GS, to l( of relay 1H opens. a circuit which is normally closed for the yellow lamp of signal 'l at frontV the closure of front contact IDS of relay 6H, suchA circuit extends from (|'),\inc1uding contact`||02 of oscillator |80C, front contact |09 of relay 6H' back contact |08 of relay 1H, winding of relay- ICP, back contact of relay 1S, and back con- The dropping away of the relay SH (see Fig; 2D) at 'the' right-hand end of the track sectionl|i-ST is eiective .to render the relay SCP active for 'the transmission of a75 code from right to `left in thetrack section 6-9'1. The circuit by' which` relay` SCP is lactive under such conditions4 extends from including contact ||3 of oscillator; C; backcontact ||4 of relay BAG, front contact ||5 of-relay"B-STR, back contact ||6 of' 'l relay SH,` .windingof relay SCP, and back contact'- It will `be seen from the mode of operation and?- thecircuit organization which has been described', that ,the tumble-down through eachY of the rebe rendered actiye only after the tumble-.down

has been completed through the stretch. By this circuit organization it is provided that the H relays are maintained picked up associated with the signals to govern passage of a train over the route being established. For example, in the con'- dition of operation under consideration the relays 2H, 4H and BH are maintained picked up during the time when the tumble-down is taking place, there being a minimum interruption in the shifting from the transmission of self-coding impulses from right to left in the track sections involved to the transmission of 180 or 75 driven code impulses. A

After the track switch 2W has been power op,- erated to its reverse position in accordancev with the closure of a reverse operating switch control circuit for the switch machine 2SM at front contact IIB of relay ZWR.r as illustrated in Fig. 4, the reverse correspondence relay ZRCR, is picked up by the energization of a circuit extending from including front contact, ||9 of relay 2WR, back contact of relay 2WN,.winding of relay 2RCR, polar contact |2| of relay 2WP in its lefthand position, and front contact |22 of relay 2WP, to (-e).

In accordance with the picking up of relay ZRCR, a circuit is closed for the energizationofv the signal control relay 2BG (see Fig. 2A) extending from (-1-), including front'contact |23 Yof front contact |25 ofrelay 2RCR, front contact |26 of relay 2H, front contact |21 of relay 2RGZ, and Winding of relay 2BG, to The picking up of relay ZBG opens the circuit by which theA red lamp of signal 2B has been energized at back contactv |28, and the closure yof front contact |28 of relay 2BG establishes a circuit by which the green lamp G of signal 2B is energized, such circuit extending from (-if), including front con-tact |28, ofv relay ZBG, front contact |29 of relay 2D, and lamp.

G ofV signal 2B, to. The relay 2D is picked up under such conditions because of the 180 driven code transmitted froml right to left in the .track section 2-5T. ASuch relay is energized only responsive to `such code by the `pulsing of contact |30 of relay 2TP, throughthe medium of trans.-

former |3| and a tuned circuit including con` Clearing of entering Signat- For the. purpose of describing specically a typical modeo' oper-.1

ation in connection with the clearing of an entering signal, it will be lassumed that an operator desires to cause the clearing of signal 8A for governing the -passage. of a train'through the siding section 8| IT associated withv the passing siding B. Under such conditions he actuates the in accordance with the application of energy at the control oflice to wire 25 with contact |35 of lever 3SML (see FiglA) in its left-hand position. The relay SWN is maintained picked up by a local stick circuit (see Fig. 1C) extending from including back contact |36 of relay SWR, front contact |31 of relay 3WN, and lowerV winding of relay 3WN, to

To cause the clearing of signal 8A (such signal being selected in preference to signal 8B by the normal position of the track switch 3W) the operator actuates the signal control lever 8-9SGL (see Fig. 1A) to its right-hand position, and in accordance with such operation energy is applied block signal.

To consider the conditions of code transmis-`V sion in the siding section of the main track associated with theV passing siding B, Fig. 2A will be considered as being placed to the right of Fig. 2D,

as the circuits of Fig. 2A correspond with thoseI provided but not shown for the right-hand end of the passing siding B.

The picking up of relay BRGZ, with the reverse switch control relay SWR dropped away, opens a circuit by which the relay SCP has been normally active for the transmission of self-coding impulses in the siding section 8-I |T. The circuit by which the relay SCP has been active extends from including front contact |39 of relay SFP, back contact of relay BRGZ, front contact |4| of relay 8-STR front contact |42 of relay 8H, winding of relay SCP, and back contact |43 of relay STR, to The cessation of the pulsing of contact |44 of relay BCP causes the track relayy at the right-hand end of the track section corresponding to relay 3TR of Fig. 2A to switch control lever 3SML (see Fig. IA) at ythe control office to its left-hand position for controlling the operation ofthe track switch SW1-at eld station No. 2 to its normal position .--lt is assumed, however, that such-trackswitch isl in its normal position in co1jrespondence'"v fith the illustration in Fig. lCV of the normally energized condition of therelay 3WN- usedv in causing the power operation o f thetrack s witch 3W to its normal position. Such relay `3WN is pickedfupl .become inactive. tion of the pulsing of relay 3TR, the failure of relay .ETP to close front contact Vcauses the relay vSFP to become inactive, and the inactivity of such relay causes the dropping away of relay 3FBP by the opening of front contact |46. The relay 3H is dropped away upon the cessation of the pulsing of contact |41 of relay 3TP, such relay being normally energized for each self-coding impulse received by the relay 3TR upon the closure of a circuit extending from includV ing front contact |41 of relay 3TP, front Contact |48 of relay 3FP, front Contact |49 of relay 3F31, winding of relay 3H, and front Contact |50 of relay 2-s'rR, to

Upon the dropping away of relay 3H, the relay 0f relay 3.31:',Y and -LaackcontactlSOf relay 3'I'ii,i i

A; the 'left-handen@ Yof the siding section,l the relay Atf1-l).V follows the,` "15j code kapplied atv the righ-hand "endof that track section, 'and the In accordance with the cessa-V pulsing of contacts |51 and |58 of relay 8TP at that rate maintains the relays SFP, BFBP and 8H steadily picked up. The relay SFP is energized during the on periods of the code; the relay 8FBP is energized during the off periods of the code in accordance with the closure of front contact |59 of relay 8FP; and the relay 8H is energized during each impulse of the code received by a circuit extending from (-i), including front Contact |58 of relay 8TP, front contact |60 of relay 8FP, front contact |6| of relay 8FBP, winding of relay 8H, and front contact |62 of relay 8-9TR, to

With the relay 8H picked up, the correspondence relay 3NCR for the track switch 3W in its energized position, and the oice controlled relay BRGZ picked up, acircuit is closed for the energization of the signal control relay SAG extending from (-1-), including front contact |63 of relay 8--9TR., front contact |64 of relay 3NCR, back contact |65 of relay .3RCR, front contact |66 of relay 8H, front contact |61 of relay 8RGZ, and winding of relay 8AG, to The picking up of relay BAG causes the extinguishing of the red lamp R of signal 8A by the opening of back contact |68, and the closure of front contact |68 causes the energization of the yellow lamp Y of such signal by a circuit extending from including front contact |68 of relay BAG, back contact |69 of relay 8D, and the yellow lamp Y of signal 8A, to This completes the mode of operation effective for causing the display of a proceed indication by an entering signal in accordance with the positioningv of the corresponding signal control lever at the control cnice.

If an operator proceeds further in the alinement of a route for an eastbound train so as to cause the clearing of the head-block starting signal |A (see Fig. 6D), the clearing of such signal is effective to cause a 180 driven code to be transmitted through the siding section 8| IT for the control of signal 8A for causing the energization of the green lamp `of such signal The clearing of the starting head-block |0A is effected in a manner corresponding to that which has been described for the clearing of the signal 2B, except that the power switch 4W at the right-hand end of the passing siding is operated to its normal position in accordance with the route desired to be established, such position being effective to select the signal |0A to be cleared in preference tothe signal |0B.

Considering again Fig. 2A being placed to the right o f Fig. 2D, the clearing of the signal |0A (see Fig. 6D) at the right-hand end of the passing siding B is effected in accordance with the envergization of a signal control relay corresponding to relay 2AG of Fig. 2A. The energization of relay 2AG under such conditions would cause the relay 3CP to become active for the transmission of a 18`0 driven code by the energization of such relay for each impulse of the oscillator |80C upon the closure of a circuit extending from including contact |10 of oscillator |800, front contact |53 of relay ZAG, front contact |54 of relay 2-3'I'R, back contact |55 of relay 3H, winding of relay 3CP, and back contact |56 of relay 3TR, to

The reception of the 180 code at the left-hand end of the track section causes the pulsing of contact |1| of relay 8TP at a 180 rate, and the puls- .ing of that contact is `effective through the medium of the decoding transformer |12 in combinationwith a tuned circuit to cause the picking up of the-relay 8D. `The picking up of such relay is effective to causeI the extinguishing of the yellow lamp of signal -BA by the openingof back contact |68, andto cause the energization of the green lamp G of signal 8Ain anl obvious manner.

Approach Zoclcing.,-'It isto be understood that Various forms of 'locking can lbe used with the present inventionA in accordance with, the requirements of practice, such locking being 'provided as straight' time locking or as approach locking with various forms of restoration for the approach locking relays AS upon passage of a train.

The approach locking illustrated in Fig. 3 for this embodiment of the present invention corresponds to that shownand described in the above mentioned prior application of Judge, Ser. No. 455,922, filed August 24, 1942, in that contacts of the H relays are used in providing the approach release for the locking.

As a typical condition of the manner in which approach locking is provided, consideration will be given more speciiically to the relay 2AS associated with the signals 2A and 2B atthe righthand end of the passing siding A. Such relay is normally energized by its stick circuit closed from including front contact |13 of relay 2M, winding of thermal relay 2TH, front contact |14 ofV relay ZAS, and winding of relay ZAS, to Upon the clearing of either signal 2A or signal 2B, the picking up of the corresponding signal control relay 2AG or 2BG is elective, in an obvious manner to cause the dropping away of the relay 2M, and the dropping away of such relay is effective to open the stick circuit forv the relay 2AS at front contact |13 to cause such relay to be dropped away. Upon the dropping away of the relay ZAS, the opening of contacts |15 and |16 of such relay in the operating circuit for the switch machine ZSM (see Fig. 4) is effective to prevent the unsafe operation of the track switch 2W. When a train accepts either of the signals, such signal is restored to stop in a manner to be hereinafter described, and the restoration of thesignal to stop; closes a circuit for the relay 2M (see Fig. 3) such circuit extending from including back Contact |11 of relay ZBG, back contact |18 of relay 2AG, and winding of relay 2M, to The closure of front contact 13 of relay 2M, with the detector track section 2.3T occupied by the train, causes the picking up of the relay ZAS by the energization of a circuit extending from `(-i) ,including front contact |13 of relay 2M, back contact |19 of relay 2-3TR, and winding of relay 2AS, to

AIf for some reason an operator desires to restore signal 2A or signal 2B to its stop position manually by the transmission of a stop code from the control ofce for such signal, he causes the transmission of a control to cause the picking up ofthe stop control relay 2--3B (see Fig. 1B), and the picking up of such relay, by opening back contact |8| in the stick circuit of relay ZRGZ, is

eiective to cause the restoration to stop of whichever of the two signals has been cleared.

The picking up of the stop repeater relay 2M y(see Fig. 3) under such conditions can cause the v|81 oflrelay 3H, front contact |88 of relay ZNCR,

and winding of relay 2AS, to( If -thiscircuit ,cannot be closed,l the relay ZAS can -be picked up onlyy after a predetermined time interval measuredl by the thermal relay The-heating coil of the thermal relay is energizedfunder' such conditions bya circuit extending from including front contact |13 of vrelay- 2M', winding of thermal relayZTH, and Yback* contact |14 of relay-2AS, to Upon theclosure of thee-ontact |89 of the thermal relay 2TH in its heated, position, the relay 2AS can be picked up by the energization of a circuit extending from (l-) 4including front contact |13 of relay 2M,- contact |89 of thermal relay ZTI-I in its heated position, and winding of relay 2AS, to The picking up of such relay upon the closure of front contact |14 establishes a stick circuit which has been describedl to maintain that relay picked up during normal conditions of the system.

1t will be noted from the typical conditions which .have been described, thatthe establishment of a route through the siding section 3T in approach to the signal 2A,.by thevdroppingaway of the relay 3H is effective to approach lock the track switch 2W so thatthe predetermined time measured by the thermal relay 2TH Visrequired upon the attempt of anoperator to restore lthe signal 2A to stop and changethe position of the track switch 2W.v

Passage ofV a train- Assuming a route to` bc established in a manner which has been described for the passage of an eastbound traininto the stretch Yof track between the passing sidings A and B from the passingV siding A, the conditions of operation will be considered that are involved in the passageof the eastbound train over such route. -v

Upon the 'acceptingof signal 2B by the eastbound train, the entrance vof the train into the detector track section 2-3T causes the dropping away of the track relay 2-3TR, and the dropping away of such relay (see Fig. 1B) prior to the dropping away of the repeater relay 2'-3TP momentarily opens the stick circuit for the relay ZRGZ at front .contact` |84 to cause' such relay to bedropped away.V lThe dropping away of the relay ZRGZ, however, cannot be elective-to render the code transmitter relayZCP (see-15kg.y 2A) active for the transmission of acode from left to right in the track section 2-"75T, as the circuit forvrelay 2CP is open atfront contact 4B 'of the relay 2`3TR for `the detector track section 2--'3T. `The dropping away of the relay ZRGZ, however, byiopening front contact |21 causes the droppingaway `of the relay 2BG, 'and the dropping away ofsu'ch relay by the'shifting of contact |28 causes the extinguishing of the green lamp of signal 2B and the 'energization of the red lamp 'of such signal. Y

When the eastbound train progresses further 'so as to occupy the track section 2+5T after the detector track section 2A3T has become unoccupied in the rear of the train, the picking up of Vthe relay ZLSTR. is effective to render the code transmitter relay 2CP active for -the transmission of a '75 code from left to right in the track section 2+5T in 'the 'rear of the train 'as indicated in the diagram f Fig. 6D. The circuit by Which the relay A2C? is energized 'for each impulse cf such code extends from including rContact |90 of oscillatorrl'lSC, backcontact |9|` of relay SAG, front contact '|512 of relay 2-'3TR, back Contact s1 of remy jzH; winding of relay l2er, and`back'contact48of relay 2'I"R `to v'The intermediate signal 4 (see Fig. 2B) clear for governingtlie passage of theeastbounditain in accordance with thetransmission of a l'll'code from right' to left in the'track section '4L-'1T vin 75 l armanner which has been described. The' green lamp of such-.signal is illuminated in accordance withthe cnergiz'a'tiori`v of a circuit extendingy from (V+), includingfront Contact |93of relay 4H, front contact |94 of relay 4D, and the green lamp G of signal 4,- to (v-)l- Y When the train progresses further along the trackway so as to occupy the track section 4'|T and leave the track section 2;-5T unoccupied in the rear of the train as illustrated in Fig. 6E, conditions of code transmission .in the track section 2-51' become effective sov as to transmit self-coding impulses from-left to right in the track section and impulses repeated from a 75 oscillator from rig-ht to left interspersed alter natelyv among the self-coding impulses. The signal is put to stop in an obviousfmanner upon the shunting of the track section 4---'|T4 by the shifting of contact |93 of relay 4H.

YUpon the droppingaway of relay 4H, due to the shunting of the track section 4-1T'by the train, the relay SCP becomes acti-ve for the trans-A mission of a '75 code bythe energization of a circuit extendingfrom including contact |95 ofoscillator 15C, iront contact |96 of relay 4S, back contact |00 of relay 4H; back contact 6| of relay 5H, winding of relay SCP, back contaci; 62er relay 5S, and back contact152 of relay 5TR, to It will be noted that the relay 5H is deenergized at this time because of its circuit Y being openat back contact 51 of relay 4S.

The .reception at the left-hand end of the track section 2-5T 'of a 75 code impulse causes thepicking up respectively of the relays ZTR, 2TP kand ZFR (sec Fig. 2A), but the relay 2H is not picked up until the reception of the second impulse. During. the 01T period 'following the rst impulse transmitted, the relay 2FBP' is picked up by the energization of an obvious circuit, and the vpicking upof suchrelay conditions the circuit for relay 2H so that such relay will be picked up upon the reception-of the -second impulse. In accordance with the picking up of the relay 2H during the second impulse received at the left-hand end'of the track section 2-^5T-, the relay 2CP is conditioned Ifor the transmission of a 'self-coding impulse', such relay being picked up upon the closure of back Contact 48 of the track relay ZTR fat Vthe terminationv rof the code impulse transmitted from right to left 'in the track section, such circuit corresponding to that which has been described as being eiective for the transmission of self-codingimpulses under the normal conditions of the system.

TheA reception vof the lright-hand end of the track section 2:-'5T ofA 'alself-coding impulse un- 'der such conditions 1causes the picking up of relays SIR, STP and 5FlD (see Fig. 2B)l respectively, and the picking up of the relay STR, lby opening back contact 52 in vthe 'circuit 'for relay 5CP, is effective to cause the 'relay 15GP 'to' be rendered inactive until the 'termination o'fthe relatively long self-coding impulse.

With reference "to the diagrams of Fig. 8, it

will be noted that 'the-/self-codin'g impulse being `relay tra (see Fig. 12B) inthe circuit'for relay `SCP to ren'de'r fthe" y y y SGPnon-respon'sive'to such second impulse; itwill'be' noted withreference to Fig. 8 that the r`terininati'cm'of the first jof the self-coding impulses transmittedis during an off period of the 75 oscillator at the right-hand end of the track section 2-5T, and therefore there is a short 01T period in the -transmission of codes in the track section 2-5'1 preceding the transmission of the next impulse i-'rom right to left in that track section. Such impulse is of a length ,measured by the 75 oscillator, the relay ECP being picked up at the beginning of the third '75 pulse of the oscillator 15C `as indicated by the dotted line |91. The picking up of the relay ECP, by the closure of front contact 5| (see Fig. 2B) in the track circuit for track section 2--5T, causes the transmission of a 75 code impulse which, upon being received at the left-hand end of the track section 2.-5T, is eiective to initiate a cycle of operation corresponding to that Which hasv been described by which a self-coding impulse is caused to be transmitted upon the termination of that. 75 code impulse.

In this manner it will be readily apparent that 4when the track section 4-'| T is yoccupied by an 1 veastbound train, and the track section 2-5'1 has become unoccupied in the rear of the train, selfucoding impulses and impulses measured by a 75 oscillator are alternately transmitted in opposite directions through the track section 2-5T as diagrammatically illustratedl in Fig. 8, theimpulses being transmitted in such a manner as not to allow the transmitters for the respective ends of the track section to fore-shorten the impulses transmitted from the opposite endof the track section. It will be noted that under such conditions the relay 5C? is active for the transmission of impulses .formed by a 75 oscillator rather thanA self-coding impulses because the relay 5H is maintained dropped away, its pick-up circuit being dependent upon the. restoration of the stick relay 4S. Such stick relay is maintained picked up when the track section 4-1T is occupied by an eastbound train by the energization of its stick circuitextending from including back contact |98 of relay 4FBP, front contact |99r of relay 4S, and winding of relay 4S, to The relay 4S has sufliciently slow drop-away characteristics to insure that it will be maintained picked up during the shifting of the contacts of relay 4FBP upon the opening of the pick-up circuit for such relay and the closing of its stick circuit at contacts 18 and A| 98 respectively.

. To considerfurther progress of the train, it Awill be assumed that it accepts the signal 6 Which has been cleared in a manner corresponding to that which has been described for the intermediate signal 4, and proceeds to a point Where the track section 4-1T becomes unoccupied in V,the rear of the train as illustrated in Fig. 6F.

Under such conditions, the conditions of code vtransmission in the track section 4-1T are established to correspond to those conditions which have been described in detail for the track section ZfST, such conditions involving the trans-- mission of a rst 75 code impulse from right to 'left causes the picking up of relays MTR, 4TP and 4FP.(see Fig. 2B) respectively at the left-hand of period the relay 4FBP is picked up.1 The picking up of such relay opens thestick circuit for relay 4S at back contact |238 and causes such relay to be dropped away, as` the pick-up circuit vfor relay 4S is open at back contact 'I9 of relay 5FBP. Upon the dropping away of the relay 4S, the circuit which has been described for the relay 5H is closed at back contact 5l to provide that `such relay is picked up. In accordance with the picking up of the relay 5H, the shifting of contact 6| in the circuit for relay SCP opens the circuit by which the relayrSCP has been active for thetransmission of impulses measured by a '75 oscillator, and closes a circuit, which has been described when considering the normal conditions of code transmission in the track section 2-5T, by whichthe relay SCP becomes active for the transmission of self-coding impulses. l It will be noted that the nature of the self-coding is such as to be dependent upon the reception of a code impulse for rendering the transmission of a code impulse in the opposite direction in the track section effective. Thus it is desirable, in order to insure the continued transmission of self-coding impulses in the track section 2-,5T, that the relay 5CP be shifted to the control for self-coding impulse transmission at a time when the relay SFP is picked up in order to insure that a circuit Y will be closed at front contact 60 of relay l.iFP

for the ltransmission of the first self-coding imcondition is insured by theuse of Contact 6| of relay 5H in the shifting of the control circuit of relay ECP to the self-coding circuit, as the relay 5H, under such conditions, would be picked up upon the reception of a self-.coding impulse by the relay ETR, the relay 5FP also being responsive to such impulse and thus being picked up at the time when the shift in the circuits for the relay ECP is rendered effective.

To consider further progress of an eastbound train, it will be assumed that the train accepts the entering signal 8A, such signal having been cleared in a manner which has been described. Upon the acceptance of such signal, the dropping away of the track relay 8-9'I'R for the detector track section 8-9T causes the dropping away of the oce controlled relay 8RGZ by opening the stick circuit for such relay at front contact 200 prior to the closure of back contact 20| of relay 8--9TP (see Fig. 1C) The dropping away of the track relay S-STR also causes the dropping away of the signal control relay 8AG (see Fig. 2D) by Y the opening of front contact' |63, and thereby causes the extinguishing of the green lamp G of signal 8A and the energization of the red lamp R of such signal upon the shifting of contact Hi8 of Yrelay BAG. The dropping away of the ofce control relay 8RGZ by 'opening front contact |61 in the circuit for relay BAG provides that signal 8A will be maintained at stop after the detector track section 8-9T has become unoccupied in the rear of the train. Y

The dropping away ofthe'track relay B-BTR is also effective to render the-code transmitter relay QCP inactive by opening its circuit at front contact ||5.

Inasmuch as the relay SCP'at the left-hand end of the track section S-S'I' cannot transmit until a code has been transmitted from right to left in the track section E-STyto cause the dropping away of the stick relay SS, there is no code transmitted in either direction in the track section feria of the track section, and during the fonowing `7.5 lfifi?? until after Athe detector track section 8-19'1 

